Mucilage formation in selected taxa of the genus Artemisia L. (Asteraceae, Anthemideae)

The myxocarpic diaspores of Artemisia taxa are characterized by the presence of mucilage cells in the achene coat, which differ between taxa and subgenera in shape and arrangement, and the ability to form a mucilage envelope after hydration. A detailed analysis of 38 taxa revealed three main achene behaviours related to achene coat structure and the modes of water retention after hydration. The most common achene coat possessed mucilage cells which formed a mucilage envelope after hydration; normally developed mucilage cells were able to produce mucilage after wetting. In taxa where the mucilage cells were riot present in the achene coat, water was gathered under a loosely adhered achene coat or in the spaces between the covering trichomes. Myxocarpic diaspores were mostly observed in taxa occurring in dry habitats, whereas taxa devoid of the ability to produce mucilage grew predominately in mesotropic habitats. The ability to form a mucilage envelope was also related to the ploidy level. The shape and arrangement of the mucilage cells in the achene coat may differ between taxa and subgenera. In Tridentatae, the mucilage cells were dispersed in groups, forming a characteristic pattern. The role of myxocarpy in the dispersal and distribution of the Artemisia taxa is discussed.